Future Developments in Stainless Steels Containing Niobium Andrew Backhouse Outokumpu Stainless Ltd Sheffield, UK
Future Developments in Stainless Steels Containing Niobium Andrew Backhouse Outokumpu Stainless Ltd Sheffield, UK
Stainless Steels Niobium Brown-Firth Harry Brearley Outokumpu Produced first commercial scale Sheffield cast of stainless Firth Vickers steel in Sheffield August 1913 British Steel Corporation In this bright future you can’t forget your past - Bob Marley British Steel Stainless The City of Sheffield ….is understood by all as the Avesta Sheffield undisputed origin for the foundation of the knowledge that ended up in the development of…steels containing niobium Tadeu Carneiro, CEO of CBMM, 2014 Outokumpu 3
Outokumpu operates around the world Tornio Avesta Kemi Degerfors Nyby Sheffield Bochum New Castle Krefeld & Benrath Shanghai Calvert Dillenburg Wildwood Richburg Dahlerbrück San Luis Potosí Integrated melt shop, hot and cold rolling Other mills Mine To be closed Service center
Outokumpu Stainless Steel Production Other Duplex 3% 3% Ferritic Austenitic 19% (CrNi) 58% Austenitic (CrNiMo) 17%
Balanced customer base across industries Consumer Other goods & 12% Medical Heavy 17% industries 8% Automotive 9% Architecture, Building & Metal Construction processing & 10 % Tubes 27% Chemical, petrochemical and energy 17 %
Austenitic 304 is all around us
Stainless Steel in Commercial Kitchens 8/18/2015 8
Requirements of Stainless Steels in professional catering equipment • Surface Finish and Appearance o Uniform, consistent & smart appearance o Low surface roughness & no crevices at joints • Corrosion resistant o No rust spots during use o Resistant to foodstuffs eg acidic foods such as vinegar & salt (eg soup) o Resistant to cleaning fluids & disinfectants, many of which contain strong chlorine based bleaches • Two grades predominate today in UK o 304, 1.4301; ~18Cr, 8Ni austenitic stainless steel o 430, 1.4016; ~17Cr ferritic stainless steel
Greater corrosion risks with 430 grade
Roping in 430 grade ferritic stainless steels • Surface roughening that occurs during cold working ( eg deep drawing) operations • Strong directional furrows become visible only after forming Caused by: Texture development in • the sub-structure - non-equiaxed & unfavourable orientation of grains Poor surface appearance • Time consuming & high cost to • remove by polishing 8/18/2015
Roping Index indicates polishing need High RI (7.5) Low RI (0.9) • Outokumpu has developed a Roping Index (RI) that is based 15 on advanced surface profile measurements 10 • A sophisticated technique for 5 Profile height (µm) roping intensity evaluation 0 • The Roping Index is used for process development, -5 benchmarking, customer support and quality control -10 purposes -15 0 10 20 30 40 50 60 70 80 Profile length (mm)
Weldability of standard ferritic stainless steels Sensitization - formation of chromium carbides; loss of corrosion resistance in 430/1.4016 Embrittlement - martensite formation in standard 430/1.4016 - development of very large grains {“Elephant Grains”} in the Heat Affected Zone.
CORE 1.4622 Ferritic Stainless Steel • Basic Concept: A new ferritic stainless steel that can be a low cost alternative to 304L/1.4307 in “everyday” applications. o Pitting corrosion resistance equal or slightly better than grade 304 o Good weldability of cold rolled wide sheet o Ability to produce excellent surface finish, including deep drawn components C C Cr Cr Ni Ni Ti Ti Nb Nb CORE 304L/1.4307 0.025 18 8 - - CORE 1.4622 0.020 21 - 0.1 – 0.7 0.1 – 0.7
Niobium & Titanium Stabilisation • Acting jointly together to produce (Ti, Nb) (C, N) particles Help produce favourable crystallographic texture during hot rolling of • slabs o in combination with controlled casting & hot rolling process parameters Produce roping-free surfaces after forming Easily polished • Prevent Sensitisation - Retain good corrosion resistance after welding • Control (Reduce) level of grain growth in weld HAZ - Adequate ductility Cube shaped particle of (Ti, Nb) (C, N) with small particles of NbC attached Cube side is 3µm (Nooning et al, 2001)
Roping Index below 1 – Virtually roping free Lower RI ensures less polishing Roping Index (RI) is needed after deep-drawing 4.5 3.0 0.3 Core 4622 Moda 430 430 (market average)
Corrosion Resistance Salt spray testing can be used to compare performance of different grades 1.4016 / 430 1.4307 / 304L 1.4622 14 day Neutral Salt Spray test ISO 9227 (5% NaCl at 35°C) Surface Finish: Outokumpu Phoenix Brushed surfaces
Corrosion Resistance Cyclic salt spray test, 100 hours 1.4509/441 (18% Cr) 1.4301/304 (18%Cr, 8%Ni) 1.4622 (21% Cr) 5% NaCl 5 min spraying, 55 min drying at 35°C, humidity 70%
Corrosion Resistance Pitting potential 316L/ /444 304L/ 441/ 430/ 409/ Relative values of pitting corrosion potential in 0.02M NaCl as a function of PREN
Weldability Relative pitting corrosion potential in 0.02M NaCl Pitting corrosion resistance • of autogenous TIG weld similar to parent metal 1.4509/441 1.4307/304L 1.4622 • Stabilization prevents precipitation of Cr carbides
What is the advantage of 1.4622 ? • Save money • Stainless Steel sold on a two-part price: Tot otal al Price e = Base e price e + Al Alloy y Sur urcharge harge (Al Alloy y Adjus ustm tment ent Factor or) Average European Base se Price: 304L 2mm thick cold rolled sheet: € 1070 0 per tonne ne • (Beginning of July 2015, Source: Steel First)
Alloy Surcharges
Alloy Surcharges
Alloy Surcharges Source : www.outokumpu.com
What are the advantages of CORE 1.4622 ? o Save money o Increase likelihood of selection of stainless steels over plastics & coated mild steels o Reduce threat from “stainless look - alike” materials o Improved environment and more sustainable option o Reduced use of the Earth’s nickel resources, compared to 304 grades o Encouragement of use of stainless steel promotes sustainability of resources: • Long life stainless steel lasts longer than less durable alternatives • Stainless Steel is itself 100% recyclable at end-of-life • “New” stainless steel from Outokumpu contains 80% recycled material
Primary Raw Material for Stainless Steel Recycled Scrap
Adages in stainless steel Adag age e - defin inition ition “a traditional opinion that is accepted by many as true or partially true” 1. 1. The general ral public ic view: w: “Stainless Steel is one type e of material and it is completely rust – pr proo oof in all circumstances” 2. The catering trade buyer’s view: “Stainless Steel occurs in two forms ms . There is a non-ma magn gneti tic stainless steel (the best st type that is completely rust-proof), and there is a magne netic tic type that is cheaper, not as good, and might go slightly rusty sty over time”
Applications • Many possibilities for stabilised ferritic stainless steels in catering equipment • Flat panel fabrications Deep drawn & polished cookware •
Applications “Light/medium weight” welded fabrications & structures Mine rescue chamber (under construction) Stainless steel for fire resistance; no paint coating required Courtesy: HEAT-IT
Applications for 1.4622 Mine rescue chamber installed and ready for use 8/18/2015 31
Summary • Niobium-Titanium stabilised Ferritic Stainless Steel CORE E 1. 1.4622 4622 can be a good alternative to standard 304L in many everyday applications • The metallurgy & processing operations are proven and understood • There are significant cost advantages over 304L • This helps increased use of stainless steels in general o which leads to a more sustainable and environmental friendly world
Contact Details Andy Backhouse Technical Manager, Outokumpu Stainless, Sheffield Andy.backhouse@outokumpu.com +44 (0) 114 2613879
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